Fix #1160 Links in README don't render properly on PyPi project page

[seratch]

Summary

This pull request resolves #1160. You can check the current state here: https://pypi.org/project/slack-sdk/ ("Getting started tutorial" section)

Category (place an x in each of the [ ])

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.signature (Request Signature Verifier)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.models (UI component builders)
• slack_sdk.scim (SCIM API client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.rtm_v2 (RTM client)
• /docs-src (Documents, have you run ./scripts/docs.sh?)
• /docs-src-v2 (Documents, have you run ./scripts/docs-v2.sh?)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[codecov]

Codecov Report

Merging #1163 (d539030) into main (afa40ea) will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1163      +/-   ##
==========================================
- Coverage   86.62%   86.57%   -0.05%     
==========================================
  Files         110      110              
  Lines       10774    10774              
==========================================
- Hits         9333     9328       -5     
- Misses       1441     1446       +5     

Impacted Files	Coverage Δ
slack_sdk/socket_mode/builtin/internals.py	70.22% <0.00%> (-2.23%)	⬇️

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[filmaj]

Looks good. The table of contents links are still broken but I am not sure how we can fix that, as the pypi-generated page based off the readme does not include any anchor IDs or other ways that we can programmatically jump to heading sections of the page 😞

[seratch]

The table of contents links are still broken but I am not sure how we can fix that,

Yes, I also noticed this but we can fix it once we find a good way to go.

Thanks for the review!